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Topic 10.2 – Fields at work – AHL
Formative Assessment
NAME: _________________________________ TEAM:__
THIS IS A PRACTICE ASSESSMENT. Show formulas, substitutions, answers (in spaces provided) and units!
The following questions are about gravitational potential energy, potential, and potential gradient.
1. Define gravitational potential. _________________________________________________________
__________________________________________________________________________________
2. Find the change in gravitational potential in moving from Earth’s surface to 3 Earth radii (from
Earth’s center).
2. _________________
3. The gravitational potential in the vicinity of a planet changes from -0.85×107 J kg-1 to -0.79×107 J kg-1
in moving from r = 1.80×107 m to r = 1.82×107 m. What is the gravitational field strength in that
region?
3. _________________
Four point masses, each of which has a mass of 875 kg, are arranged in a circle of
radius 2250 m as shown.
4. What is the gravitational potential at the center of the configuration?
4.
_________________
5. What is the work done by gravity in bringing a 150-kg mass from very far away to
the center of the configuration?
5. _________________
The following questions are about escape speed and orbital speed about a planet whose rotational
period is 15.5 hours.
6. What is the escape speed from a planet whose mass is 2.001026 kg and whose radius is 4.00×107
m?
6. _________________
7. What is the orbital speed about this planet at an altitude of one planet radius?
7. _________________
8. Using Kepler’s 3rd law find the period of a satellite that is three planet radii above the surface.
8. _________________
9. At what altitude would a satellite be if it were in synchronous orbit about the planet?
9. _________________
The following questions have to do with the energy of an orbiting mass.
10. Sketch graphs showing the
variation with orbital radius of the
kinetic
energy,
gravitational
potential energy and total energy
of a satellite. Be sure to include all
graphs on a single energy vs. radius coordinate system. 10._in graph_
The following questions are about electrostatic potential energy, potential, and potential gradient.
11. Define electrostatic potential energy. ___________________________________________________
__________________________________________________________________________________
12. Calculate the electrostatic potential 1.75×10-10 m from a proton.
12. ________________
13. The electrostatic potential in the vicinity of a charge changes from -2.87 V to -2.54 V in moving from
r = 2.82×10-3 m to r = 2.85×10-3 m. What is the electric field strength in that region? Is the charge (-)
or is it (+)? _____.
13. ________________
An equipotential surface caused by a charge is shown to
the right.
14. Find the electric field strength at the point P. The
vertical axis is measured in J C-1 and the grid lines in
the x and y directions are in cm.
14. ________________
15. Find the electric field strength at the point Q. How
can you visually tell the field is stronger at P than it is
at Q?
15. ________________
___________________________________________
P
Q
16. How do you know that this surface is not caused by a mass?
__________________________________________________________________________________
The following questions are about an electron moving in an electrostatic field.
17. An electron is brought from infinity to a distance of 1.75 mm from a charge of -285 C. How much
work was done by the electrostatic field on the electron? Does your answer depend on the path
taken by the electron? ________.
17. ________________
18. An electron moves from a point in space where the potential is 100.0 V to another point where the
potential is 200.0 V. If it started from rest, what is its speed at the end of this trip?
18. ________________
A diagram showing equipotential surfaces set up by some sort of a charge
configuration is shown.
19. Find the electric field strength at the points A and B.
19. ________________
20. What is the force acting on an electron if placed at the point A? Which way does it point?
20. ________________
________________
21. Describe a physical scenario in which such a field could be set up in a lab.
Topic 1.1 – Measurements in physics
Formative Assessment
NAME: _________________________________ TEAM:__
__________________________________________________________________________________